The present invention relates to a control method and apparatus for air conditioners, and more particularly, but not exclusively, to a control method and apparatus suitable for an automobile air conditioner wherein the temperature of air flow is automatically controlled in accordance with change of the heat load in the passenger compartment of an automobile.
As shown in FIG. 1, a conventional control system for an air conditioner comprises a set circuit 1 for producing an output signal indicative of a desired temperature T.sub.set of air in a compartment or region to be conditioned, a temperature sensor 2 for producing an output signal indicative of the actual temperature T.sub.r of air in the compartment, and a detector 3 responsive to the output signals from set circuit 1 and sensor 2 for detecting any deviation between the desired temperature T.sub.set and the actual temperature T.sub.r and for producing an output signal indicative of the detected deviation. A temperature controller 4 receives the output signal from detector 3 to control the temperature of air flow in accordance with the deviation so as to adjust the actual temperature T.sub.r to the desired temperature T.sub.set and maintain it at the same.
During operation of temperature controller 4, the sensor 2 acts to produce a feedback signal indicative of any change of the actual temperature in the compartment, and the controller 4 acts to adjust the actual temperature T.sub.r to the desired temperature T.sub.set in response to the feedback signal from sensor 2. In this instance, the heat load in the compartment fluctuates in accordance with variations of the outside ambient temperature T.sub.am, and subsequently the actual temperature T.sub.r fluctuates due to delay of heat transfer in the compartment. To restrain fluctuation of the actual temperature in the compartment, an outside ambient temperature sensor 6 and an adder 7 are provided to preliminarily compensate the fluctuation of head load caused by a change of the outside ambient temperature T.sub.am.
In the control system described above, assuming that the quantity of air flow is at a constant value, the temperature of air flow is adjusted by controller 4 as represented by the following equation. EQU T.sub.ao =K.sub.set .multidot.T.sub.set -K.sub.am .multidot.T.sub.am -K.sub.r .multidot.T.sub.r +C
where T.sub.set is the desired temperature in the compartment, T.sub.am is the outside ambient temperature, T.sub.r is the actual temperature in the compartment, C is a constant, and K.sub.set, K.sub.am and K.sub.r are respectively gains of set circuit 1 and sensors 6 and 2, which are preliminarily determined to adjust the actual temperature T.sub.r toward the desired temperature T.sub.set without any influence caused by changes of the outside ambient temperature. In controlling the air conditioner, although the outside ambient temperature is measured to compensate the temperature of air flow in accordance with fluctuation of the heat load in the compartment, it is disregarded to compensate the temperature of air flow in relation to another fluctuation of the heat load caused by the intensity and direction of sunshine entering the compartment, change of the vehicle speed and the number of passengers and the like, since the constant C is experimentarily determined in a fixed value. This results in any deviation between the actual temperature and the desired temperature due to the disregarded fluctuation of the heat load.